1. Field of the Invention
The present invention relates to processes for flattening an end section of a tube.
2. Description of Related Art
Processes for making the end sections of tubes flat are used to enable the tubes to be connected in an end-to-end fashion. This connecting can be performed by arranging the flattened ends of two tubes next to one another and then welding them to one another, or by making bores through the flattened tube ends and then screwing the tube ends together with a screw going through these bores.
Supporting frames, scaffolds, braces, etc. made of tubes, in particular metal tubes, can be made from the noted types of connected tubes. In such environments, the mechanical strength of the connection of the tubes to one another, as well as of the tubes to other structural parts of the structure in question, is an essential design feature.
However, in flattening the end section of a tube, in which the tube wall is, usually, pressed together over a certain area at the tube end, problems appear relating to the fact that the greater the wall thickness of the tube, as compared to its diameter, and with increasing strength of the tube material, the greater is the danger that the end section of the tube will tear when the tube wall is flattened. The flattened end section of the tube, then, consists of two flat metal parts with dangerous burrs that can spread further apart from one another.
This problem is serious, in particular, in tubes for frame structures, since the latter consist of very strong and durable materials, and thus, tear very easily when the end sections are pressed together.
Tests have shown, for example, that when flattening the end section of a tube made of a strong aluminum alloy with 60 mm outer diameter and 5 mm wall thickness to form even, flat parts with a size of at least 40.times.40 which are, later, to be provided with bores for receiving a threaded Joint, the biggest bulges appears, during the flattening of the tube wall, at two opposite points on the tube periphery at a distance of about 35 mm from the face of the tube. Starting at these points, tears form that propagate radially inward and axially in both directions. These tears finally reached even the face of the tube.
The flattened end section of the tube consisted finally of two more or less evenly split parts spread apart from one another. Such tube ends are unsightly and dangerous because of the sharp burrs. Further the danger exists that the existing tears may continue to grow.